(AK) classA HA/Preamplifier.

[gommer]

Alex, is the transformer in a separate box?

By the looks of it, yes, all 2 of them. This a a completely separated constructed beast, from PS to output

[Deleted]

Is any one here willing to build one for a third party?

Hi Mrarroyo

if you've built tube amps before (as i have) then I'm pretty sure (if the third party is you) that you could manage to build the Class A.

it's my second SS amp (SCHA was the first) and with help i managed.

i think you would love this HA and was kind of wondering why you had not jumped in earlier.

OK IMHO and not intended to be in anyway insulting to you or any other members.

DIY amps are for people who DIY.

it starts to get fraught with difficulties building for third parties. what happens if something fails. Mr (or Mrs) third party can't fix it and it starts to get complicated with amps yoyoing back and forth. so just an opinion and others may feel differently.

however i would be happy to help any one build for themselves and have done in the past.

it's much more fun to have a go and build. after 20 years i still get a buzz out of switching on fir the first time and finding that ''it works''.

being a newcomer should not matter. build the SCHA to get the hang of things and then armed with a bit more confidence do the Class A. I've been building with tubes for 20 years but still built the SCHA first just to get used to all of those small parts and it really did help with the Class A build.

i know you do a bit of DIY so it should be no problemo for you and you would be in great company (myself not included).

so any more interest

we could think on another group buy. i would be up for organizing boards and so forth if the interest was there.

so no insult intended just a very personal take on things

take care

[mrarroyo]

I think I will pass at building SS amps. For some reason I can mod tube amps with no problems but I am all thumbs in SS gear.

[Will]

Feb 24, 2011 22:55:08 GMT @sandyk said:

Class A HA with Will's PCBs.



P.S.
Ian (Rabbit)
You would love the bottom end with your 701s.
It goes Loooow !
Alex

Alex, that looks really nice and tidy, good stuff!

I've stuffed resistors in mine so far, doing a bit at a time. Having a class A already built up does take the urgency off for me

How's everyone else doing?

[XTRProf]

Feb 25, 2011 21:00:33 GMT mrarroyo said:

I think I will pass at building SS amps. For some reason I can mod tube amps with no problems but I am all thumbs in SS gear.

Actually, this AHA is something like a kit already as Will had kindly put away all the difficulties on a PCB. It's not like putting it togather on a vector board.

Sourcing for parts can be a little hassling if you go through the diy shops way as not all of them carry the parts you need. But the webstores will be easier as it's all letting your hand and mouse clicks do the talking. Of course, also empting your credit card do the talking.

[Deleted]

Hi All

Well here it is my box of snakes build and as you can see from the picture I was not exaggerating about my lack of metalworking skills.



I had a number of design goals in mind when I started the build.

1) relay switched inputs as close to the RCA’’s as possible
2) input connections as short as possible
3) no wires under the signal boards
4) to run the amp as cool as possible
5) to not let my lack of ability get in the way of enjoying the HA/PRE
6) function over form

So armed with a 400x300x80 Peasante Hifi 2000 case with 10mm front panel I took my best shot at achieving the above.

It’s the sort of quality work that makes Britain what it is today.

Just a word on the case

Not the most glamorous case but I would rather stuff up a cheap case than an expensive one. The nice thing is that when my skill level and confidence grow the case can be changed. I opted for the 80mm high case because I wanted plenty of air around the OP transistor heat sinks and can see no reason to squash things in just to use a smaller case (and I’m too old for finger yoga). I know there are some eddy current issues with using a steel case but I’m not sure what eddy currents sound like.
.
This is a real piece of Hifi not an accessory and deserves its space on my rack on SQ alone.

Signal

I was fussier about the input side of things because I figure any noise on the input gets amplified by the following stages. So short was best for me and explains why I’ve orientated the boards the way I have. I’ve used 0.5mm twisted pair (sounds like a good name for an audio company) solid silver for signal input and 1mm solid for the OP both are PTFE (yup I like silver and with the big smoothy DACT it sounds superb).




Relays

The input relays have their regs removed to allow stacking and are run from a 12@2.5a switch supply. These are big boards and I’m glad I decided to stack them JLH style.they are switching both input and ground which is nice.



The wiring

Hmmm I’ve used plain Jane cables for the Power and grounds. I’ve not found that using special cables here sounds any better so I don’t use them. I’ve used the power/ground bottom of the case and signal top in the same way that I build with tubes. For the power connectors I’ve gone for twisted triple with screen connected at the AC PSU end and BNC plugs.



LED's

I don’t like them so none on the front panel but it’s useful to know when the power is on when the case top plate is off. I soldered mine directly on to the reg boards. I think that Wills execution of his Led’s was one of the best I’ve seen so I may try that in the future when I know a bit more.

The DACT has raised some issues around how to ground it but it’s not serious and I’m on the case (no pun intended) with that.

Things to try

I’m just so happy with the sound that all I really want to try is some of those naked resistors but no rush for that.

Very few of my tube amps made it into cases and even then it was wooden frame and Ali top plate so this is really all new to me.



my 76/45 under developement with cheap hamond trafo's

So that’s about it

take care

My first proper SS build.

‘’ I guess it shows I took the blows and did it my way’’

I’m here to learn so please, any constructive comments would be most welcome.

Just a big thanks to all who have contributed to this amazing thread. I really am so lucky to have had such fine company on this build... I know from what I’ve seen and read here that I’m building with the BIG hitters and it’s been a privilege to get to know you all.

I’ve learned so much

I will be making my personal thanks to Alex and Will when we all have something to cheer about.

Keep going with the builds you’re going to love this amp as much as I do.

Take care

[Deleted]

Hey Shaun,

What's all this

Well here it is my box of snakes build and as you can see from the picture I was not exaggerating about my lack of metalworking skills.

Looks damn fine to me! You wait until my rats nest appears!

Sadly not even started yet , too much boring stuff getting in the way!

[Will]

Indeed! Nice work Shaun, I'm glad that you are enjoying it so much.

Are those the input relay boards from eBay? They look just the job.

[Deleted]

Feb 26, 2011 16:25:10 GMT Will said:

Indeed! Nice work Shaun, I'm glad that you are enjoying it so much.

Are those the input relay boards from eBay? They look just the job.

Hi Will & Chris

yes this build has been a real Hifi Highlight for me and a real ear opener. I'd discounted SS as unmusical after listening to lots of the stuff over the years. i used to get invites from a well known UK company beginning with L to have a listen to their latest kit. that stopped when i said the sound was awful. i also remember listening to some expensive Chord stuff again dry, unmusical and boring.

the Class A IMHO is one of those amps that transcends the Valve vs SS thing. it's just plain superb and a pleasure to listen to especially with the K701. i keep having a quick listen just to make sure things are really that good and end up on 3 hour sessions. as i say just superb.

the relay boards came from Audiowind and yup more LED's to hide. they work well and are pretty good price wise. i think it was Alex that suggested trying them and he posted a link further back in the thread.

i have a pair of those two input relays which i intend to turn round to get one input and two out per channel to switch load resistors 68r and 120r.

as for the build

well the nice thing about DIY is that we all end up with something that reflects our skill level.

when my diy improves so will the casework.

the hard bit has been done for us by yourself and Alex who really deserve most of the credit.

thanks for the nice comments Will & Chris it's made me feel a little less like a twit.

Chris you could always use mine as a how not to guide

take care

[Deleted]

This morning I hooked up my Function Generator and C.R.O. to the HA and checked both channels individually with Square Waves between 20 HZ and 100 KHZ. Possibly due to the use of an attenuator instead of a dual potentiometer, I was very surprised to see that the 100KHZ squarewave was still very good, as was the 20HZ squarewave . I did not go below 20HZ, as my function generator has a drop in the quality of it's waveform below that.
With the 100KHZ squarewave there were a few small spikes evident at the output of the other channel. Short circuiting the input of the channel not being tested eliminated that completely.
It appeared to be minor breakthrough via the attenuator and the thin S-VHS cabling that I am using from the Inputs to the attenuator, and the attenuator to the input terminals.
All testing was done at my typical listening level setting of the attenuator.
Alex

[Will]

Alex, that's an excellent result. My hearing is not too good up at 100kHz ( ), but knowing that it's technically capable across a wide bandwidth is good, and shows the stability of the design.

It seems that a few people are looking at using this HA as a pre-amp. Due to lack space, and an impending power amp of a certain provenance ( ), I'm combining pre-amp capability into my Class A. I've a paper sketch of how I will build the signal switching on veroboard, but I needed to be able to select these options on the front panel.

Originally my amp looked like this:






With a power led on left, a volume knob in a counter-bored hole and headphone socket.

With the hugely appreciated help of Mick, I now have another counter-bore in the front panel, in place of the power led, with indicator leds at 30 degree positions. I've used a matching knob to complete the change. Mick also cleaned up my less than adequate hand counter-sink of the headphone socket hole. Mick, thanks again, you are a star!



The input switching will be arranged with one additional set of RCA inputs, with position 1 being primary input to headphone socket direct, input and output relays unenergised, 2 primary input to RCA out, output relays energised. Third position is secondary input to headphones, input relay energised, and fourth position is secondary input to RCA out, with both sets of signal relays energised. It makes sense to me, anyway!

Anybody else doing the pre-amp thing?

[Deleted]

Feb 26, 2011 13:32:38 GMT @shaun said:

Hi All

Well here it is my box of snakes build and as you can see from the picture I was not exaggerating about my lack of metalworking skills.



I had a number of design goals in mind when I started the build.

1) relay switched inputs as close to the RCA’’s as possible
2) input connections as short as possible
3) no wires under the signal boards
4) to run the amp as cool as possible
5) to not let my lack of ability get in the way of enjoying the HA/PRE
6) function over form

So armed with a 400x300x80 Peasante Hifi 2000 case with 10mm front panel I took my best shot at achieving the above.

It’s the sort of quality work that makes Britain what it is today.

Just a word on the case

Not the most glamorous case but I would rather stuff up a cheap case than an expensive one. The nice thing is that when my skill level and confidence grow the case can be changed. I opted for the 80mm high case because I wanted plenty of air around the OP transistor heat sinks and can see no reason to squash things in just to use a smaller case (and I’m too old for finger yoga). I know there are some eddy current issues with using a steel case but I’m not sure what eddy currents sound like.
.
This is a real piece of Hifi not an accessory and deserves its space on my rack on SQ alone.

Signal

I was fussier about the input side of things because I figure any noise on the input gets amplified by the following stages. So short was best for me and explains why I’ve orientated the boards the way I have. I’ve used 0.5mm twisted pair (sounds like a good name for an audio company) solid silver for signal input and 1mm solid for the OP both are PTFE (yup I like silver and with the big smoothy DACT it sounds superb).




Relays

The input relays have their regs removed to allow stacking and are run from a 12@2.5a switch supply. These are big boards and I’m glad I decided to stack them JLH style.they are switching both input and ground which is nice.



The wiring

Hmmm I’ve used plain Jane cables for the Power and grounds. I’ve not found that using special cables here sounds any better so I don’t use them. I’ve used the power/ground bottom of the case and signal top in the same way that I build with tubes. For the power connectors I’ve gone for twisted triple with screen connected at the AC PSU end and BNC plugs.



LED's

I don’t like them so none on the front panel but it’s useful to know when the power is on when the case top plate is off. I soldered mine directly on to the reg boards. I think that Wills execution of his Led’s was one of the best I’ve seen so I may try that in the future when I know a bit more.

The DACT has raised some issues around how to ground it but it’s not serious and I’m on the case (no pun intended) with that.

Things to try

I’m just so happy with the sound that all I really want to try is some of those naked resistors but no rush for that.

Very few of my tube amps made it into cases and even then it was wooden frame and Ali top plate so this is really all new to me.



my 76/45 under developement with cheap hamond trafo's

So that’s about it

take care

My first proper SS build.

‘’ I guess it shows I took the blows and did it my way’’

I’m here to learn so please, any constructive comments would be most welcome.

Just a big thanks to all who have contributed to this amazing thread. I really am so lucky to have had such fine company on this build... I know from what I’ve seen and read here that I’m building with the BIG hitters and it’s been a privilege to get to know you all.

I’ve learned so much

I will be making my personal thanks to Alex and Will when we all have something to cheer about.

Keep going with the builds you’re going to love this amp as much as I do.

Take care

That looks a very nice build to me Shaun, so stop doing yourself down, you seem to be more than happy with its SQ, so mission accomplished. VERY WELL DONE.

Mick.

[Deleted]

Feb 27, 2011 14:55:27 GMT Will said:

Alex, that's an excellent result. My hearing is not too good up at 100kHz ( ), but knowing that it's technically capable across a wide bandwidth is good, and shows the stability of the design.

It seems that a few people are looking at using this HA as a pre-amp. Due to lack space, and an impending power amp of a certain provenance ( ), I'm combining pre-amp capability into my Class A. I've a paper sketch of how I will build the signal switching on veroboard, but I needed to be able to select these options on the front panel.

Originally my amp looked like this:






With a power led on left, a volume knob in a counter-bored hole and headphone socket.

With the hugely appreciated help of Mick, I now have another counter-bore in the front panel, in place of the power led, with indicator leds at 30 degree positions. I've used a matching knob to complete the change. Mick also cleaned up my less than adequate hand counter-sink of the headphone socket hole. Mick, thanks again, you are a star!



The input switching will be arranged with one additional set of RCA inputs, with position 1 being primary input to headphone socket direct, input and output relays unenergised, 2 primary input to RCA out, output relays energised. Third position is secondary input to headphones, input relay energised, and fourth position is secondary input to RCA out, with both sets of signal relays energised. It makes sense to me, anyway!

Anybody else doing the pre-amp thing?

Looks great Will, pleased your happy with it, looks the business.

ATB. Mick.

[Will]

pleased your happy with it, looks the business.

Very pleased and very happy with how it looks, Mick!


Hi Shaun,

I've just noticed your manly looking switch/attenuator brackets and connectors. Care to share where you got them from?

[Deleted]

My hearing is not too good up at 100kHz ( ), but knowing that it's technically capable across a wide bandwidth is good, and shows the stability of the design.

Hi Will
Don't forget that it was square wave , not sine wave, which means that bandwidth is quite a bit higher than 100KHZ. This means that it is suitable for playback of 24/192 high resolution files.
I didn't check the -3dB point, as my function generator only goes to 300KHZ (in a fashion!)
Alex

[Deleted]

Feb 27, 2011 20:12:42 GMT Will said:

pleased your happy with it, looks the business.

Very pleased and very happy with how it looks, Mick!


Hi Shaun,

I've just noticed your manly looking switch/attenuator brackets and connectors. Care to share where you got them from?

Hi Will

The shaft couplers came from ebay I'll see if i can find a link.

they where listed as 6mm router stepper motor couplers (glad i did not have to say that in one breath). if you punch in 6mm shaft couplers in ebay you should find them (£9 for three). what i really like about them is the nice BIG grub screws which allow a nice tight lock (i just hate having to keep taking the lid off to re tighten those weedy ones). i think that they came from Thailand(naturally) i do have a spare if you want to try one. i must admit to taking a bit of a punt on them but they fit 6mm like a glove. i did enjoy the coooolness of them when i opend the pack.

the shafts are from good old B&Q. £8 for a meter of 6mm Ali doweling. I've used the B&Q stuff for years and it's good value and there's no twist in it just solid as a rock. it has a heatshrink jacket as it can like most metal) ring a bit so damping sorts that IMHO.

I'll go and have a look to see what i can find

take care

[Deleted]

hhhhhhhh Hi Will

I've ran back as fast as i can and here's the things

cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=330338706319&ssPageName=STRK:MEWNX:IT

Your front panel is just lovely work.

the brackets for the switch and Switcher are hacked out of 3mm Ali that i used for tube amp top plates. angle brackets back and front to keep things nice and solid. i just don't like any movement there it just puts a strain on the switch and feels UN-nice.

i've just checked the link and it's fine

take care

[XTRProf]

Feb 10, 2011 20:05:51 GMT Will said:

Pin out of the LS devices

Just a quick check, which PTHs did you guys used for the LS devices? The outer or inner diameters? I'm going to put some "valve" sockets there so that I can easily swab between the test transistors and the LS devices after everything becomes stable. Also, I don't have to do any more solder work at those positions should the transistors kaput under use.

[XTRProf]

Feb 19, 2011 0:00:25 GMT @sandyk said:

BTW, when using OPA134 for the Offset corrector I.C. and a 3K resistor terminating the input, DC Out has been measured as 0mV
on Jeff's and my own PCBs.
Alex

So do you suggest using this BB instead of the AD744? Thanks.

[Deleted]

Feb 28, 2011 7:34:26 GMT XTRProf said:

Feb 19, 2011 0:00:25 GMT @sandyk said:

BTW, when using OPA134 for the Offset corrector I.C. and a 3K resistor terminating the input, DC Out has been measured as 0mV
on Jeff's and my own PCBs.
Alex

Do you suggest using this BB instead of the AD744? Thanks.

Chong
Considering that it is also readily available from places like R.S. for <AU$3 each , yes .The AD744 is likely to be very hard to obtain these days as it is now quite an old I.C.
Alex

[Deleted]

which PTHs did you guys used for the LS devices? The outer or inner diameters?

I used the outer holes, as on my PCBs at least, there appeared to be more copper around the outer holes due to the masking used.
The LS devices will not go kaput unless there is a catastropic failure due to fault code "ID ten T". *
They are used well below their ratings.


* Write it down in alpha numeric form.

[Deleted]

Why the DACT 2 is likely to sound a little better than the generic Asian attenuators.


I mentioned in a previous post about a small amount of breakthrough to the other channel when testing with a 100KHZ Square Wave. Shaun mentioned a further improvement when using the DACT CT2, which I believe is likely to be due to better HF separation with the DACT 2 ,due to much greater wafer separation with the DACT 2.
Alex

(Click on photo to enlarge.)

Attachments:

[Deleted]

The input switching will be arranged with one additional set of RCA inputs, with position 1 being primary input to headphone socket direct, input and output relays unenergised, 2 primary input to RCA out, output relays energised. Third position is secondary input to headphones, input relay energised, and fourth position is secondary input to RCA out, with both sets of signal relays energised. It makes sense to me, anyway!Anybody else doing the pre-amp thing?

Hi Will

yes makes perfect sense to me and I'm sure judging from your previous work will be well executed.

Just out of interest how will you be powering the relays?

i have another set of 2 way relay boards on order to switch outputs from RCA to HP with the appropriate load R's.

I'd love to find a speaker amplifier of the same quality to use with the HA/Pre but i think it's going to be a struggle to find one.

cool job done by Mick on the front panel (nice one Mick it looks like you know a thing or two about working with metal ).

take care

[XTRProf]

Feb 28, 2011 7:43:53 GMT @sandyk said:

Feb 28, 2011 7:34:26 GMT XTRProf said:

Do you suggest using this BB instead of the AD744? Thanks.

Chong
Considering that it is also readily available from places like R.S. for <AU$3 each , yes .The AD744 is likely to be very hard to obtain these days as it is now quite an old I.C.
Alex

Oh, I didn't know that the BB op amp is newer than the AD. However, the AD is still more expensive than the BB although it is older. Perhaps, the BB path is a better bet since it is a newer op amp with perhaps some improvements over the AD. Anyway, noted!

[XTRProf]

Feb 28, 2011 7:49:22 GMT @sandyk said:

which PTHs did you guys used for the LS devices? The outer or inner diameters?

I used the outer holes, as on my PCBs at least, there appeared to be more copper around the outer holes due to the masking used.

You got a point there! Also, becasue I'm going to "socket that area" I will need as much space as possble between pins for a better job done as well.